From mboxrd@z Thu Jan  1 00:00:00 1970
From: Asdo <asdo@shiftmail.org>
Subject: Re: Why does one get mismatches?
Date: Sat, 20 Feb 2010 00:34:43 +0100
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To: Neil Brown <neilb@suse.de>
Cc: Piergiorgio Sartor <piergiorgio.sartor@nexgo.de>, Steven Haigh <netwiz@crc.id.au>, Bill Davidsen <davidsen@tmr.com>, Bryan Mesich <bryan.mesich@ndsu.edu>, Jon@eHardcastle.com, linux-raid@vger.kernel.org
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Thank you for your explanation Neil,

Neil Brown wrote:
> When memory changes between being written to one device and to another, this
> does not cause corruption, only inconsistency. Either the block will be
> written again consistently soon, or it will never be read.

This is the crucial part...

Why would the filesystem reuse the same memory without rewriting the 
*same* block?

Can the same memory area be used for another block?
If yes, I understand. If not, no I don't understand why the block is not 
eventually rewritten to contain equal data on both disks.

Is this a power-fail-in-the-middle thing, or it can happen even when the 
power is always on?

Do I understand correctly that raid-456 is instead safe ("no-mismatch") 
because it copies the memory region?

Thank you